As an exhaust gas analysis system adapted to analyze exhaust gas, there has been known a system that includes an exhaust gas dilution device adapted to dilute exhaust gas with diluent gas and an analyzer adapted to measure components contained in the diluted exhaust gas produced by the exhaust gas dilution device.
More specifically, as the exhaust gas dilution device, a device adapted to control a flow rate of the diluted exhaust gas to a constant flow rate (hereinafter also referred to as a setting flow rate) is used, such as a constant flow rate dilution sampling device, and by changing the setting flow rate, a ratio in flow rate between the exhaust gas and the diluent gas, i.e., a dilution ratio can be changed.
As the analyzer, an analyzer configured to be able to change an analysis range in order to analyze exhaust gases diluted at various dilution ratios by the above-described exhaust gas dilution device is used.
The above-described configuration enables the exhaust gas to be analyzed in accordance with each set of various analysis conditions such as a model of a vehicle and a driving mode by changing the setting flow rate and the analysis range.
Meanwhile, in general, in order to ensure analysis accuracy in this sort of exhaust gas analysis system, the analysis accuracy is verified using predetermined reference gas before analyzing exhaust gas.
As a method for the verification, there is known a method called a propane shot described in, for example, Engine emission measurement handbook, pp. 27 to 28, in which specifically, propane gas having known density is supplied to an exhaust gas analysis system in place of exhaust gas to evaluate the recovery rate of the propane gas.
In the above-described verification, for example, in order to analyze the concentration of propane gas within an analysis range preset in an analyzer, it is necessary to dilute the propane gas at an appropriate dilution ratio, and to do this, a supply flow rate of the propane gas should be appropriately set on the basis of a setting flow rate and the analysis range.
However, since the setting flow rate and the analysis range are ones that are appropriately changed in accordance with a set of analysis conditions as described above, to ensure analysis accuracy in any of various sets of analysis conditions, the propane shot should be performed at a different supply flow rate for each of many combinations obtained by multiplying the number of setting flow rates and the number of analysis ranges by each other, requiring a great amount of time and effort.
The above-described problem is common to exhaust gas analysis systems including an exhaust gas dilution device adapted to dilute exhaust gas to produce diluted exhaust gas, such as a bag mini-diluter in addition to a constant flow rate sampling device, and an analyzer adapted to measure components contained in the diluted exhaust gas.